The present invention relates to electronic keyless entry systems and in particular to a passive keyless entry system that is particularly adapted for use with automotive vehicles.
Automotive keyless entry systems, when first introduced, typically included a numerical keypad located on the exterior door panel of the vehicle. The operator entered a unique multiple digit code on the keypad to automatically unlock or lock the vehicle. Recently, more sophisticated keyless entry systems for vehicles have been proposed which use a portable remote transmitter that is carried by the operator and a receiver located in the vehicle that is adapted to unlock the vehicle in response to the detection of a coded radio frequency signal or a coded optical signal received from the transmitter. Such systems require that the operator actuate a button or switch on the transmitter to initiate the transmission, similar to the operation of a conventional automatic garage door opener, in order to conserve battery life and prevent inadvertent actuation.
While more convenient to operate than the keypad-type keyless entry systems, the latter transmitter/receiver-type systems nonetheless require that the operator physically locate the transmitter and actuate a button to unlock the vehicle. Hence, the convenience provided by such a system versus a conventional key and lock arrangement is not substantially improved.
In addition, while other types of "keyless" entry systems are known and presently used in other applications, these systems for various reasons are generally not suitable for automotive use. This would include systems employing magnetic card readers, interrogation/transponder-type systems, and conventional automatic garage door openers. A magnetic card-type system is probably adaptable to automotive use, but provides little added benefit to justify the expense. Interrogator/transponder-type systems, though adaptable to operate in a totally passive manner, are more complex and therefore more expensive, and present a power consumption problem as the interrogator therefore must be on and interrogating at all times. In addition, the transponder in such systems must be capable of receiving as well as transmitting data, thus adding to cost. Lastly, automatic garage door systems, while appearing to employ similar technology have substantially different operating requirements which result in significantly different circuit designs. In particular, an automotive keyless entry system must possess a level of noise immunity and signal discrimination that is substantially greater than that required for an automatic garage door opener. This is due to several factors including the many different environments in which vehicles may be located, the greater number of vehicles that may be equipped with comparable systems, and the fact that large numbers of vehicles are frequently located within close proximity to one another, such as in parking lots. In addition, automatic garage door systems require that the operator actuate a transmitter, and therefore are not totally passive. Also, garage door opener-type systems have a substantial range and therefore can potentially activate a function, such as unlocking the trunk of the vehicle, when the operator is some distance away from the vehicle and unaware the trunk has been opened.
Accordingly, it is the primary object of the present invention to provide a totally passive keyless entry system that is especially adapted for use with automotive vehicles.
It is also an object of the present invention to provide an automotive keyless entry system that is adapted to automatically unlock the vehicle as the operator approaches the vehicle.
In addition, it is an object of the present invention to provide a passive keyless entry system having a beacon/transmitter that is extremely small in size and includes a motion sensing switch that automatically activates the transmitter in the beacon whenever movement of the beacon is sensed.
It is a further object of the present invention to provide a passive keyless entry system that employs electronic circuitry which permits the system to function in the micropower range while in its quiescent state.
Additionally, it is an object of the present invention to provide a passive keyless entry system having an acceptable operating range between the beacon and receiver while providing a projected beacon battery life in excess of one year.
Further, it is an object of the present invention to provide a passive keyless entry system that employs signal transmission and coding techniques which provide a high level of noise immunity and signal discrimination.
It is a further object of the present invention to provide a passive keyless entry system having special anti-theft capabilities featuring a continuously changing coded transmission at predetermined intervals and a programming capability to synchronize the coded beacon transmission with the receiver.
It is also an object of the present invention to provide a passive keyless entry system that is reliable and yet is relatively inexpensive to manufacture.
In general, the passive keyless entry system according to the present invention comprises three basic components: a transmitter or beacon, a receiver/controller, and a receiving antenna. The beacon, which is small enough to be attached to a keychain, is carried by the operator and incorporates a motion sensor that is used to energize the transmitter portion of the beacon. The transmitter in the beacon is adapted to emit a coded radio frequency signal that contains a clock code, an identification code and function information, and an error correction code. Since the coded signal includes a clock code, the coded signal changes at predetermined intervals. The beacon is designed to continue to transmit repeatedly its coded signal until no motion is detected for a predetermined period of time. Thus, the motion sensor serves to promote beacon battery life and enables the present system to function in a totally passive manner.
The receiving antenna comprises a simple coil of wire, wound to be sensitive at the transmitted frequency of the beacon. The antenna is located at a position on the vehicle to optimize the performance of the system. It has been found desirable to adapt the system so that the receiver/controller is responsive to the signal from the beacon when the beacon comes within 3-6 feet of the vehicle.
The receiver/controller is mounted inside the vehicle and is adapted to operate on the vehicle's 12 volt negative ground battery. Upon receipt of a radio frequency signal from the antenna, the receiver/controller is adapted to process the coded radio frequency signal and evaluate the serial data contained therein. If the signal is determined to be valid, the receiver/controller automatically unlocks the driver's-side vehicle door. The receiver/controller also includes a clock which is originally synchronized with the clock code of the beacon. The receiver/controller will automatically resynchronize the receiver's clock to the clock code of the transmitted signal each time a valid signal is received. In addition, a tolerance algorithm will be incorporated in the receiver/controller such that the received coded signal will be valid within a predetermined tolerance depending on the time from the last reception of a valid beacon signal.
Optionally, the beacon may be provided with function switches which, when depressed by the operator, change the function code contained in the radio frequency signal, thus directing the receiver/controller to open the vehicle trunk and/or perform other functions.
In addition, the receiver/controller in the present system is adapted to automatically lock the vehicle doors when the operator leaves the vehicle and carries the beacon out of range of the receiver/controller, assuming the proper status of the ignition and doorjamb switches.
The passive keyless entry system further includes a program mode by which the coded signal can be sent from the beacon to the receiver/controller in an uncoded format. The clock of the receiver/controller is originally synchronized with the clock signal of the beacon when the system is in the program mode. In the program mode, the receiver/controller can also resynchronize the uncoded clock and identification code signal from the transmitter with the clock in the receiver and store the clock and identification code in the receiver/controller. The program mode can also store a plurality of identification and clock codes in the receiver.
Additional objects and advantages of the present invention will become apparent upon reading the following description of the preferred embodiment of the present invention which makes reference to the drawings in which: